1. Field of the Invention
The present invention relates to a guide actuator fit to be applied on machining tools, robotics, electrical equipments and automation industry, and so on, especially to a new one having U-shape guide structure and enabling to bear higher radial load.
2. Description of the Prior Art
Commonly known linear guide actuators are mainly composed of a pair of parallel linear slide rails fastened on an assistant frame, a movable table locked on a table of the linear slide rail, and a screw or a belt used as an actuating structure to drive the table to move back and forth (as U.S. Pat. No. 5,598,043). The assistant frame is usually made of cast iron, but it is more difficult in manufacturing process and more expensive in cost. Therefore, some designs are made of extruded aluminum for reducing cost. The aluminum material is soft enough to be extruded as every kind of shape to reduce process cost. However, aluminum has low stiffness such that linearity and parallelism are relatively more unstable. In this way, it is essential to adjust carefully and pay more attention to the assembling geometry precision.
FIG. 6 is a prior improved design (U.S. Pat. Nos. 5,273,381 and 5,277,498). The design uses a U-shape guide structure (1) made of iron and steel but not linear slide rails and an assistant frame. A pair of grooves (16) are respectively set at the inner walls of two sides of the U-shape guide structure, and there are steel balls (8) set in the grooves to guide the table (2) slide directly along the grooves (16) of the guide structure. Because the U-shape guide structure is made of steel and iron, the design has better intensity. Besides, the structure of the design is simple such that time and requirement of experience of users for assembly are reduced. However, when the improved design bears weight, or withstands a downward force (as F shown in the figure), both walls of two sides of the U-shape guide structure would spread out slightly due to withstanding steel balls such that the table (2) slightly descend. Therefore, the precision of the guide actuator is lowered to affect the stiffness of the mechanism and positioning accuracy. Unfortunately, most guide actuators are set in this way, including the single axis type and two axes type, X-Y actuator. The X-Y actuator according to this way bears force from upside to underside. As long as the mechanism on the table is too heavy or the table bears too much load downward, the precision of the actuator would be affected obviously. Moreover, the actuator may bears too heavy load to be destroyed.
Besides, there is another type of transmission mechanism such as one disclosed by U.S. Pat. No. 4,659,238 by the name of “Linear Guideway”. It is essentially installing a block on a rail, then afterwards fasten a table onto the block such that the table is movable with respect to the rail. Since the rail provided in this case is designed to configure into a narrow, elongated small cross section element whose cross sectional moment of inertia is very small, the rail is apt to be distorted and flexed causing inconvenient to assemble. Moreover, the planarity of the base entraining the mechanism greatly affects the parallelism of table movement. Because the actuating means is not included in this prior art so that an extra actuating means must be required to connect with the block thereby requiring an extra space in the mechanism to accommodate actuating means. As a result production efficiency of the machine will be greatly lowered by spending too much labor force for calendering and caliberating the base.